Solid state light sources are not yet frequently used for general illumination due to limitations in operating temperature, color rendering performance, color consistency, and efficiency. By way of example, solid state light sources with an input power range of 10 W to 40 W have a high operating temperature and accordingly require the use of relatively large heat spreaders and cooling structures. Moreover, LEDs have a limited spectral bandwidth, and thus, color rendering performance is limited due to only a limited number of efficient phosphors that have been found. Additionally, the use of phosphors in proximity to the LED limits the choice of phosphors due to temperature and chemical incompatibility. Color consistency is also problematic due to production tolerances in the wavelength conversion materials application process and variations in the wavelength conversion materials itself. Finally, compared to conventional gas discharge lamps, the cooling efficiency of conventional solid state light sources is low and, thus, large cooling structures are required.
The source of solid state light sources, e.g., LEDs and lasers, operate at low temperature (in the range of 60°-200° C.) relative the temperature of the sources in other types of lighting, e.g., the filament in an incandescent bulb, the cathodes in a gas discharge base fluorescent lamps, or the plasma in an high intensity discharge lamp. The high temperature of these conventional sources causes most of the heat generated by the lamp to radiate to ambient and spread out over a large area. The lower operating temperature of LEDs, which results in less heat radiating to ambient, renders it difficult to use LED lamps in existing lighting fixtures at same input power as conventional light sources because the LEDs require higher capacity cooling structures. Fortunately, in most cases, the input power of LED systems can be lower than that used for conventional light sources, as state of the art LEDs have become more efficient than incandescent lamps (in produced light output versus electrical power in), and soon will become more efficient than the gas discharge based conventional lamps, but cooling efficiency remains a factor in adopting solid state light sources.
The engineering and manufacturing investments required to overcome the challenges in solid state light source applications renders that the costs of solid state illumination installations high compared to that of conventional light source solutions. As a result, the introduction of an efficient and environmentally safe solid state illumination technology has been delayed. Accordingly, what is desired is an illumination device, which includes solutions to many of the drawbacks mentioned before, and which can be used and installed in the existing infrastructure.